ISO/TR 19402:2018

TECHNICAL ISO/TR
REPORT 19402
First edition
2018-08
Paints and varnishes — Adhesion of
coatings
Peintures et vernis — Adhérence des revêtements
Reference number
ISO/TR 19402:2018(E)
©
ISO 2018

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ISO/TR 19402:2018(E)

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© ISO 2018
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Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Adhesive strength tests without scratch/cut . 3
4.1 Tests with mechanical stress application on the coating . 3
4.1.1 Pull-off test . 3
4.1.2 Twist-off test . 5
4.1.3 Peel-off test 1 . 6
4.1.4 Peel-off test 2 . 8
4.2 Tests with continuous deformation of test specimens . 9
4.2.1 Bend test with a wedge-shaped conical mandrel . 9
4.2.2 Bend test with a conical mandrel .11
4.2.3 Bend test with a cylindrical mandrel 1 .12
4.2.4 Bend test with a cylindrical mandrel 2 .14
4.2.5 Three point bending method .15
4.2.6 T-bend test 1 .17
4.2.7 T-bend test 2 .19
4.2.8 Cupping test 1 .20
4.3 Test with impact stress application .22
4.3.1 Single-impact test 1 .22
4.3.2 Single-impact test 2 .25
4.3.3 Single-impact test 3 .27
4.3.4 Single-impact test 4 .28
4.3.5 Falling-weight test 1 .30
4.3.6 Falling-weight test 2 .33
4.3.7 Falling-weight test 3 .35
4.3.8 Multi-impact test 1 .36
4.3.9 Multi-impact test 2 .38
4.3.10 Multi-impact test 3 .41
4.3.11 Multi-impact test 4 .43
4.3.12 Impact-bend test .44
5 Adhesive strength tests with scratch/cut .45
5.1 Tests with single scratch .45
5.1.1 Scratch test 1 .45
5.1.2 Scratch test 2 .46
5.1.3 Scratch test 3 (Scrape-adhesion test) .47
5.2 Test with multiple scratch (without deformation of test specimens) .49
5.2.1 Pressure-water jetting test .49
5.2.2 Cross-cut test 1 .53
5.2.3 Cross-cut test 2 .56
5.2.4 Cross-cut test 3 .57
5.2.5 X-cut test 1 .58
5.2.6 X-cut test 2 .58
5.2.7 X-cut test 3 .59
5.2.8 X-cut test 4 .59
5.2.9 Scribe test with a square-diagonal grid .60
5.2.10 Scribe test with a rhombus grid .61
5.3 Test with multiple scratch (with deformation of test specimens) .62
5.3.1 Cupping test 2 .62
6 Evaluation methods for adhesive strength .63
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6.1 Auxiliary methods .63
6.1.1 Contrasting 1 .63
6.1.2 Contrasting 2 .64
6.2 Visual methods.64
6.2.1 Failure pattern analysis.64
6.2.2 Comparison of areas .65
6.2.3 General assessment .66
6.3 Instrumental methods .67
6.3.1 Digital image evaluation 1 .67
6.3.2 Digital image evaluation 2 .67
Annex A Synoptical tables for the methods.69
Bibliography .76
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee
SC 9, General test methods for paints and varnishes.
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Introduction
The determination of the adhesive strength is one of the most important preconditions for evaluating
the protective function of coatings.
This document offers a helpful overview for the selection of the test method most suitable for each
individual case in regard to the evaluation of the adhesive strength.
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TECHNICAL REPORT ISO/TR 19402:2018(E)
Paints and varnishes — Adhesion of coatings
1 Scope
This document summarises the common methods for evaluating the adhesive strength of coatings on a
substrate, which can be another coating beneath or the substrate itself. The test methods and evaluation
methods are described in Clauses 4, 5, and 6. In the case of standardized test methods the respective
standard is referenced in regard to procedure and evaluation. Annex A compares the methods in the
synoptic Tables A.1, A.2, and A.3.
Often the adhesive strength cannot be sufficiently evaluated by means of a single method.
The purely physical methods for measuring the adhesive strength are such in which mechanical
quantities (e.g. force or torsion moment) are measured directly.
All other methods are based on the evaluation of behaviour under mechanic stress according to practical
conditions. For these methods the viscoelastic properties have a wide influence on the evaluation of the
adhesive strength, so that it can only be tested comparatively within one method.
Each method has its specific application. An unsuitable method can lead to false information. All of the
test methods for the evaluation of the adhesive strength require a certain routine of the test person,
especially in regard to identifying the separation line. For most of the test methods the test results,
among other things, depend on the film thickness of the coating to be tested. In addition, for several
methods differences between tests on a test sheet and in practice can occur, due to different roughness
of the substrate.
Effects of delamination caused by weathering or corrosion influences are not subject of this document.
In case cohesion failures predominantly occur during an adhesive strength test, this is no measure for
the adhesive strength. However, information can be given on the protective effect of the coating against
corrosion.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4618, Paints and varnishes — Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
adhesion
phenomenon of attachment at the interface between a solid surface and another material caused by
molecular forces
Note 1 to entry: Adhesion should not be confused with cohesion.
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[SOURCE: ISO 4618:2014, 2.7]
3.2
cohesion
forces that bind a film or coat into an integral entity
Note 1 to entry: Cohesion should not be confused with adhesion.
[SOURCE: ISO 4618:2014, 2.55]
3.3
adhesion failure
detachment of a coating from the substrate caused by external forces
Note 1 to entry: The substrate can be another coating beneath or the working material.
3.4
cohesion failure
loss of coherence within a coating caused by external forces
3.5
adhesive strength
force required to detach a coating from a substrate or another coating
[SOURCE: ISO 4618:2014, 2.8]
3.6
wet adhesive strength
adhesive strength (3.5) immediately after previous exposure to moisture
3.7
separation line
interface in which adhesion failure (3.3) occurs
3.8
failure pattern
entirety of the visual coating defects, which are caused by an adhesive strength (3.5) test
3.9
failure pattern assessment
classification of a failure pattern (3.8) by means of criteria or reference patterns
3.10
failure pattern analysis
quantitative evaluation of a failure pattern (3.8) with specification of the relative percentages of area
for adhesion failure (3.3) and cohesion failure (3.4) as well as the separation line(s)
3.11
main separation line
separation line with the largest area
3.12
repeatability conditions
conditions where independent test results are obtained with the same method on identical test items
in the same laboratory by the same operator using the same equipment within short intervals of time
[SOURCE: ISO 5725-1:1994, 3.14]
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3.13
repeatability limit
r
the value less than or equal to which the absolute difference between two test results obtained under
repeatability conditions (3.12) may be expected to be with a probability of 95 %
[SOURCE: ISO 5725-1:1994, 3.16]
3.14
reproducibility conditions
conditions where independent test results are obtained with the same method on identical test items in
different laboratories with different operators using different equipment
[SOURCE: ISO 5725-1:1994, 3.18]
3.15
reproducibility limit
R
the value less than or equal to which the absolute difference between two test results obtained under
reproducibility conditions (3.14) may be expected to be with a probability of 95 %
[SOURCE: ISO 5725-1:1994, 3.20]
4 Adhesive strength tests without scratch/cut
4.1 Tests with mechanical stress application on the coating
4.1.1 Pull-off test
— Principle
A uniformly increasing tensile force is applied to a test cylinder (metal cylinder of diameter
20 mm), which is adhered to the coating, until the test cylinder is pulled off. The pull-off strength
is determined by calculating the tensile force to pull off the test cylinder and the area of the test
cylinder.
The principle of the pull-off test is illustrated schematically in Figure 1.
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Key
1 substrate
2 coating
3 adhesive film
4 free punch
5 test cylinder
6 outer ring to support the test panel
a
The pull-off direction.
Figure 1 — Principle of the pull-off test
— Application
The pull-off test is generally applicable.
— Procedure
— Attach the test cylinder to the coating by means of a previously tested adhesive.
— Cut the coating around the circumference of the test cylinder using a suitable tool through to
the substrate (see Figure 1).
— Attach the test specimen to the test apparatus so that it is supported and the test cylinder is
connected to the pulling unit, centred and without being wedged.
— Carry out the pull-off process with a uniformly increasing tensile force and measure when the
test cylinder is pulled off.
— Evaluation
The test result is the pull-off strength (MPa) = the tensile force when pulling off the test cylinder
divided by the area of the test cylinder.
Specify the result of the failure pattern analysis (see the procedure specified in 6.2.1).
— Precision
Precision data are not available at present.
— Reference
The pull-off test is specified in ISO 4624 and ISO 16276-1.
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4.1.2 Twist-off test
— Principle
By means of a motor-driven test apparatus a uniformly increasing torsion moment is introduced to
a test cylinder (a metal cylinder of a 12 mm or 15 mm diameter and a 6 mm drill), which is adhered
to the coating, until it is twisted off. The adhesive strength (“shear strength”) can be read directly
2
from the test apparatus as shear stress (N/mm = MPa).
Figure 2 illustrates the principle of the twist-off test in a schematic diagram. Figure 3 shows the
minimum distance between the test cylinders for repeated tests.
Key
1 substrate
2 coating
3 adhesive
4 test cylinder
a
The axis of rotation.
Figure 2 — Principle of the twist-off test
Figure 3 — Minimum distance between the test cylinders
— Application
The twist-off test is generally applicable.
— Procedure
— Use a sufficiently thick substrate (minimum 0,7 mm) or a substrate with reinforcement adhered
to the backside in order to avoid deformation during testing.
— Adhere the test cylinder to the coating using a previously tested adhesive. For repeated tests
observe a minimum distance between the test cylinders (see Figure 3).
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— Attach the test apparatus at the hexagon bolt of the test cylinder (see Figure 2) and secure the
test panel against twisting.
— Start torsional stress and read the shear stress from the apparatus when the test cylinder is
twisted off.
— Evaluation
2
The test result is the shear stress (N/mm = MPa), which is read from the apparatus and interpreted
as the twist-off strength.
Specify the result of the failure pattern analysis (see the procedure specified in 6.2.1).
— Precision
Precision data are not available at present.
— Reference
The twist-off test is specified in Reference [50].
4.1.3 Peel-off test 1
— Principle
A fabric specified by material, thread size, and mesh size is bedded into a newly applied coating
material. After curing of the coating a tensile tester grabs the overlapping fabric, and due to
continuous tensile force at 90° the coating is peeled off from the substrate. The peel strength is
determined as the force required for peeling off and referring to the width of the test specimen.
Figure 4 schematically shows the peel-off process and the function of a 90°-peel-off apparatus.
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Key
1 substrate
2 coating
3 fabric
4 tape (uncoated end of the test panel)
a
The direction of movement of the test panel.
b
The direction of rotation of the pressing roller on the coating.
c
The direction of rotation of the pressing roller on the uncoated test panel.
d
The direction of peel-off (tensile tester).
Figure 4 — Principle of the peel-off test 1
— Application
The peel-off test 1 is preferably carried out on automotive coatings.
— Procedure
— Coat the test panel (dimensions 15 mm × 100 mm) sparing a 10 mm wide strip at the edge of
the narrow side. Subsequently bed the fabric so that it remains for about 50 mm uncoated and
overlaps at the uncoated end of the test panel (see Figure 5).
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Key
1 substrate
2 coating
3 fabric
4 tape (uncoated end of the test panel)
Figure 5 — Test panel with coating and fabric
— After drying/hardening of the coating mount the test panel into a tensile tester equipped with
a 90°-peel-off apparatus (see Figure 4) and clamp the free end of the fabric.
— Start the peel-off process and record the tensile force (peel strength) required for peeling off.
— Evaluation
Determine the mean peel strength over a peel-off distance of at least 50 mm for five test specimens,
disregard the beginning and the end of the test.
The test result is the mean value (with standard deviation) from the five individual determinations,
which is designated as the peel strength (N/15 mm width of test specimen).
Specify the result of the failure pattern analysis (see the procedure specified in 6.2.1).
— Precision
Precision data are not available at present.
— Reference
The peel-off test 1 is specified in Reference [47].
4.1.4 Peel-off test 2
— Principle
The coating is peeled off from the substrate under specified conditions by means of an electrically
driven test apparatus. The force is determined which is required for peeling off and which refers to
the width of peeling off. Figure 6 illustrates the peel-off process in a schematic diagram.
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Key
1 substrate
2 coating
3 peel-off tool
a
The peel strength.
Figure 6 — Principle of the peel-off test 2
— Application
The peel-off test 2 is generally applicable.
— Procedure
— Specify the peel-off tool (cutting angle/width), setting angle, peel-off speed and peel-off
distance.
— Mount the test panel into the peel-off apparatus and start the peel-off process.
— During testing record the force (peel strength) required for peeling off.
— Evaluation
Determine the mean peel strength over the peel-off distance, disregard the beginning and the end
of the peel-off process.
The test result is the mean peel strength divided by the width of the peel-off tool (N/mm).
— Precision
Precision data are not available at present.
— Reference
The peel-off test 2 is specified in Reference [35].
4.2 Tests with continuous deformation of test specimens
4.2.1 Bend test with a wedge-shaped conical mandrel
— Principle
The test panel is deformed from the direction of the substrate side by pressing in a wedge-shaped
conical mandrel of specified geometry. The smallest radius of the mandrel is determined for which
no defect of delamination in the deformed area is detectable.
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Figure 7 shows the test principle in a schematic diagram. Figure 8 illustrates the dimensions of the
wedge-shaped conical mandrel.
Key
1 wedge-shaped conical mandrel
2 test panel (after deformation)
3 elastic pad
Figure 7 — Principle of the bend test with a wedge-shaped conical mandrel
Key
R radius – the number specifies the bending radius in mm
Figure 8 — Measures of the wedge-shaped conical mandrel
— Application
The bend test with a wedge-shaped conical mandrel is preferably carried out on coil coatings.
— Procedure
— Put the test panel with the coated side onto an elastomer panel.
— From the direction of the substrate side press the mandrel by hand (with lever transmission)
or by means of a pneumatic apparatus into the panel until the deformation results in a V-shape.
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Doing so, the longitudinal axis of the mandrel shall be parallel to the direction of rolling of the
substrate.
— Evaluation
Examine the coating in the deformed area for delamination using a magnifier and determine the
smallest bending radius for which no defect can be detected.
The test result is this bend radius (mm) divided by the thickness of the substrate (mm).
— Precision
Precision data are not
...